package com.hp.ecs.xqa.util.orm;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.lang.annotation.Annotation;
import java.net.URL;
import java.net.URLDecoder;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Set;
import java.util.jar.JarEntry;
import java.util.jar.JarInputStream;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.hp.ecs.xqa.util.IoUtil;

/**
 * 王海涛介绍给范后军使用的类
 * 
 * @since 2007-12
 */
public class ResolverUtil<T> {
	/** An instance of Log to use for logging in this class. */
	private static final Log LOG = LogFactory.getLog(ResolverUtil.class);

	/**
	 * A simple interface that specifies how to test classes to determine if they are to be included in the results
	 * produced by the ResolverUtil.
	 */
	public static interface Test {
		/**
		 * Will be called repeatedly with candidate classes. Must return True if a class is to be included in the
		 * results, false otherwise.
		 */
		boolean matches(Class type);
	}

	/**
	 * A Test that checks to see if each class is annotated with a specific annotation. If it is, then the test returns
	 * true, otherwise false.
	 */
	public static class AnnotatedWith implements Test {
		private Class<? extends Annotation> annotation;

		/** Construts an AnnotatedWith test for the specified annotation type. */
		public AnnotatedWith(Class<? extends Annotation> annotation) {
			this.annotation = annotation;
		}

		/**
		 * Returns true if the type is annotated with the class provided to the constructor.
		 */
		public boolean matches(Class type) {
			return type != null && type.isAnnotationPresent(annotation);
		}

		@Override
		public String toString() {
			return "annotated with @" + annotation.getSimpleName();
		}
	}

	/** The set of matches being accumulated. */
	private Set<Class<? extends T>> matches = new HashSet<Class<? extends T>>();

	/**
	 * The ClassLoader to use when looking for classes. If null then the ClassLoader returned by
	 * Thread.currentThread().getContextClassLoader() will be used.
	 */
	private ClassLoader classloader;

	/**
	 * Provides access to the classes discovered so far. If no calls have been made to any of the {@code find()}
	 * methods, this set will be empty.
	 * 
	 * @return the set of classes that have been discovered.
	 */
	public Set<Class<? extends T>> getClasses() {
		return matches;
	}

	/**
	 * Returns the classloader that will be used for scanning for classes. If no explicit ClassLoader has been set by
	 * the calling, the context class loader will be used.
	 * 
	 * @return the ClassLoader that will be used to scan for classes
	 */
	private ClassLoader getClassLoader() {
		return classloader == null ? Thread.currentThread().getContextClassLoader() : classloader;
	}

	/**
	 * Attempts to discover classes that are annotated with to the annotation. Accumulated classes can be accessed by
	 * calling {@link #getClasses()}.
	 * 
	 * @param annotation the annotation that should be present on matching classes
	 * @param packageNames one or more package names to scan (including subpackages) for classes
	 */
	public void findAnnotated(Class<? extends Annotation> annotation, String... packageNames) {
		if (packageNames == null) {
			return;
		}

		Test test = new AnnotatedWith(annotation);
		for (String pkg : packageNames) {
			findInPackage(test, pkg);
		}
	}

	/**
	 * Scans for classes starting at the package provided and descending into subpackages. Each class is offered up to
	 * the Test as it is discovered, and if the Test returns true the class is retained. Accumulated classes can be
	 * fetched by calling {@link #getClasses()}.
	 * 
	 * @param test an instance of {@link Test} that will be used to filter classes
	 * @param packageName the name of the package from which to start scanning for classes, e.g.
	 *            {@code net.sourceforge.stripes}
	 */
	private void findInPackage(Test test, String packageName) {
		packageName = packageName.replace('.', '/');
		ClassLoader loader = getClassLoader();
		Enumeration<URL> urls;

		try {
			urls = loader.getResources(packageName);
		} catch (IOException ioe) {
			LOG.warn("Could not read package: " + packageName, ioe);
			return;
		}

		while (urls.hasMoreElements()) {
			try {
				String urlPath = urls.nextElement().getFile();
				urlPath = URLDecoder.decode(urlPath, "UTF-8");

				// If it's a file in a directory, trim the stupid file: spec
				if (urlPath.startsWith("file:")) {
					urlPath = urlPath.substring(5);
				}

				// Else it's in a JAR, grab the path to the jar
				if (urlPath.indexOf('!') > 0) {
					urlPath = urlPath.substring(0, urlPath.indexOf('!'));
				}

				File file = new File(urlPath);
				if (file.isDirectory()) {
					loadImplementationsInDirectory(test, packageName, file);
				} else {
					loadImplementationsInJar(test, packageName, file);
				}
			} catch (IOException ioe) {
				LOG.warn("could not read entries", ioe);
			}
		}
	}

	/**
	 * Finds matches in a physical directory on a filesystem. Examines all files within a directory - if the File object
	 * is not a directory, and ends with <i>.class</i> the file is loaded and tested to see if it is acceptable
	 * according to the Test. Operates recursively to find classes within a folder structure matching the package
	 * structure.
	 * 
	 * @param test a Test used to filter the classes that are discovered
	 * @param parent the package name up to this directory in the package hierarchy. E.g. if /classes is in the
	 *            classpath and we wish to examine files in /classes/org/apache then the values of <i>parent</i> would
	 *            be <i>org/apache</i>
	 * @param location a File object representing a directory
	 */
	private void loadImplementationsInDirectory(Test test, String parent, File location) {
		File[] files = location.listFiles();
		StringBuilder builder = null;

		for (File file : files) {
			builder = new StringBuilder(100);
			builder.append(parent).append("/").append(file.getName());
			String packageOrClass = (parent == null ? file.getName() : builder.toString());

			if (file.isDirectory()) {
				loadImplementationsInDirectory(test, packageOrClass, file);
			} else if (file.getName().endsWith(".class")) {
				addIfMatching(test, packageOrClass);
			}
		}
	}

	/**
	 * Finds matching classes within a jar files that contains a folder structure matching the package structure. If the
	 * File is not a JarFile or does not exist a warning will be logged, but no error will be raised.
	 * 
	 * @param test a Test used to filter the classes that are discovered
	 * @param parent the parent package under which classes must be in order to be considered
	 * @param jarfile the jar file to be examined for classes
	 */
	private void loadImplementationsInJar(Test test, String parent, File jarfile) {
		JarInputStream jarStream = null;
		try {
			JarEntry entry;
			jarStream = new JarInputStream(new FileInputStream(jarfile));

			while ((entry = jarStream.getNextJarEntry()) != null) {
				String name = entry.getName();
				if (!entry.isDirectory() && name.startsWith(parent) && name.endsWith(".class")) {
					addIfMatching(test, name);
				}
			}
			jarStream.close();
		} catch (IOException ioe) {
			LOG.error("Could not search jar file '" + jarfile + "' for classes matching criteria: " + test
				+ " due to an IOException", ioe);
		} finally {
			IoUtil.close(jarStream);
		}
	}

	/**
	 * Add the class designated by the fully qualified class name provided to the set of resolved classes if and only if
	 * it is approved by the Test supplied.
	 * 
	 * @param test the test used to determine if the class matches
	 * @param fqn the fully qualified name of a class
	 */
	private void addIfMatching(Test test, String fqn) {
		try {
			String externalName = fqn.substring(0, fqn.indexOf('.')).replace('/', '.');
			ClassLoader loader = getClassLoader();
			if (LOG.isDebugEnabled()) {
				LOG.debug("Checking to see if class " + externalName + " matches criteria [" + test + "]");
			}

			Class type = loader.loadClass(externalName);
			if (test.matches(type)) {
				matches.add(type);
			}
		} catch (ClassNotFoundException t) {
			LOG.warn("Could not examine class '" + fqn + "' due to a " + t.getClass().getName() + " with message: "
				+ t.getMessage());
		}
	}
}
